Microstructure and morphology control of potassium magnesium titanates and sodium iron titanates by molten salt synthesis

Titanates materials have attracted considerable interest due to their unusual functional and structural properties for many applications such as high-performance composites, devices, etc. Thus, the development of a large-scale synthesis method for preparing high-quality titanates at a low cost is desired. In this study, a series of quaternary titanates including K_0.8Mg_0.4Ti_1.6O₄, Na_0.9Mg_0.45Ti_1.55O₄, Na_0.75Fe_0.75Ti_0.25O₂, NaFeTiO₄, and K_2.3Fe_2.3Ti_5.7O₁₆ are synthesized by a simple molten salt method using inexpensive salts of KCl and NaCl. The starting materials, intermediate products, final products, and their transformations were studied by using TG-DSC, XRD, SEM, and EDS. The results show that the grain size, morphology, and chemical composition of the synthesized quaternary titanates can be controlled simply by varying the experimental conditions. The molar ratio of mixed molten salts is critical to the morphology of products. When KCl:NaCl = 3:1, the morphology of K_0.8Mg_0.4Ti_1.6O₄ changes from platelet to board and then bar-like by increasing the molar ratio of molten salt (KCl-NaCl) to raw materials from 0.7 to 2.5. NaFeTiO₄ needles and Na_0.75Fe_0.75Ti_0.25O₂ platelets are obtained when the molar ratio of molten salt (NaCl) to raw materials is 4. Pure phase of Na_0.9Mg_0.45Ti_1.55O₄ and K_2.3Fe_2.3Ti_5.7O₁₆ are also observed. The formation and growth mechanisms of both potassium magnesium titanates and sodium iron titanates are discussed based on the characterization results.